The invention pertains to a method for controlling the lateral guides for a metal strip, especially at the entrance or exit from rolling stands in rolling mills, for example; they can also be used in front of drive apparatus or in other strip processing lines.
Methods for automatically controlling the lateral guides for a metal strip are already known from the prior art. Such guides usually consist of two straightedges, one on each side of the strip, which are positioned by hydraulic cylinders and which can be pressed or tightened against the strip as the strip passes by. The known systems frequently also comprise a mechanical connection between the two straightedges as well as a common control system for their adjustment. Although systems of this type are relatively simple to design, the ability to adjust and to control them is very limited. Not all variations in the course of the strip can be adequately corrected, and damage to the metal strip and to the straightedges cannot always be adequately avoided.
Methods are also known in which, while a strip is passing through the guide, one of the straightedges can be operated under automatic position control, while other is pressed with a defined force against the strip. In this method, the pressing force between the straightedge and the strip is determined for both sides. While the strip is passing through the guide, the straightedge on one side is maintained in a fixed position under automatic position control. The other straightedge is pressed with a defined force against the strip under automatic force control. The nominal force of the force-controlled straightedge is prespecified as a function of the properties of the strip to be guided such as its material, width, thickness, temperature, or speed. This nominal force is selected in such a way that it is greater in all cases than the contact force of the strip on the force-controlled side, because otherwise the guide could be opened on this side by the strip. A disadvantage of this method is that, when the strip exerts a force on the position-controlled side, both this force of reaction and the prespecified force exerted by the force-controlled side must be absorbed on the position-controlled side. This leads to damage to the strip and also to the straightedges. To repair the straightedges, long system shut-downs are unavoidable. Another disadvantage of the method derives from the fact that the width of the strip to be guided is usually not constant. Because a fixed nominal force is prespecified independently of the width of the strip to be guided, the straightedges cannot be adequately adjusted to various changes in the width of the strip, as a result of which the guidance is poor in the best of cases or the forces between the strip and the straightedges are so high that considerable damage occurs.
Laid Open Application No. DE 4003717 A1 discloses another method for the lateral guidance of a strip for rolling. The goal of the disclosed method is to increase the service life of the straightedges in a roller table. For this purpose, an automatic control system is proposed for the straight edges which work in such a way that the guides can be pressed against the edges of the strip and moved away from them again in alternation. The disadvantage of this method is, among other things, that nominal values for an automatic force control circuit are prespecified by a process computer on the basis of an input, and as a result in many cases the automatic control cannot proceed with sufficient accuracy. Because the nominal forces are prespecified, this method suffers from the same disadvantages as those mentioned above, so that, when this method is applied, the straightedges still wear out more quickly than desired, and significant damage to the edges of the strip can occur.
The technical goal which arises from this prior art is therefore to be seen in making available an improved method for the automatic control of the lateral guides for metal strips or at least in avoiding one of the above-mentioned disadvantages.